How many miles does it take to upgrade a PS flight?

I'm a bit confused, maybe I've been looking at the wrong link.

This past december I used 70,000 award miles (supersaver) to book a round trip first class airfare from JFK To SFO.

Now, my firm is willing to buy a coach ticket for me, but how many extra miles would it cost to upgrade? From what I could find it seemed to use the same chart for mile prices when booking flight solely with miles, which doesn't make any sense.

Anyone know?

Thanks in advance.